The medical field utilizes highly flexible and torqueable catheters and guidewires to perform delicate procedures deep inside the human body. Endovascular procedures typically start at the groin where a catheter and/or guidewire are inserted into the femoral artery and navigated up to the heart, brain, or other anatomy as required. Once in place, the guidewire is removed so the catheter may be used for the delivery of drugs, stents, embolic devices, or other devices or agents. The catheter may be a balloon catheter used for therapy directly, either by itself or with a balloon expandable stent pre-loaded on it. A radiopaque dye is often injected into the catheter so that the vessels may be viewed intraprocedurally or in the case of a diagnostic procedure, the dye may be the primary or only agent delivered through the catheter.
Intravascular procedures, by definition, work in and with delicate anatomy, namely the vessels themselves, which are often also compromised by disease. Damage to the vessels is particularly critical to avoid. If blood in the vessels is allowed to “leak,” direct damage may be caused to any tissue outside of the normal capillary approach contacted by the blood, and/or may result in a deadly problem of exsanguination or “bleed out”. When treating an aneurysm, the control of the catheter tip is especially important. An aneurysm is a very fragile ballooned vessel wall which can easily be punctured if the guidewire or catheter is not precisely controlled.
Embolic coils are typically wound from fine platinum wire into a primary diameter sized for delivery through standard catheters. Standard catheters typically have a diameter of 0.014 inches to 0.035 inches, while embolic coils are typically wound to a 0.002 inch or 0.003 inch diameter. The coils are cut to length and a secondary shape or helix is set into the coil. The embolic coil is a device that can fill an anatomical structure. Embolic coils are usually used to fill or partially assume the shape and size of a vessel, an aneurysm, a fistula, etc. When the coil is inserted through a catheter and released into the body, the coil structure can slow or arrest blood flow, providing a surface for platelet aggregation and clot formation.
Advances in embolic coils include the addition of Dacron or polyester fibers, the addition of hydrophilic polymers, and the use of alternative shapes to standard cylindrical or helical primary coils. These advances have been designed in response to desires for improved and faster clotting (increased thrombogenicity through increased surface area) and/or blood flow arrest, better filling and/or holding force (interconnection), and greater filling density through swelling polymer post coil placement. However, these advances have not yielded demonstrable clinical benefit. In the case of the hydrophilic swelling polymer, potential negative clinical issues have manifested all the while clinical use increases. Furthermore, any perceived benefit from increased filling density from hydrophilic polymers is offset by the understanding that a water bearing surface is likely to be the least integrated into living tissue. That is, the “wet ball” surface is both geometrically and chemically the least optimal for tissue in-growth, integration, and stability.
Typically coils are made of a solid wire coil, which is wound in a “stacked” configuration, i.e. each subsequent adjoining coil strand is placed or added without any gap between the wire strands. This limits the ways in which the embolic coil may be shaped and its thrombogenic properties, among other limitations. The use of platinum embolic coils typically requires a large number of coils to occlude a volume, as platinum embolic coils do not have a high thrombogenicity. The platinum coils also tend to pack (i.e. compress in situ), reducing the effective filling of the aneurysm. This increases the risk of the aneurysm rupturing, a recurrence of the aneurysm, or another aneurysm forming near the occluded aneurysm. As such, it would be desirable to have improved embolic coils.